A thin ring of radius R has charge q uniformly spread on it. The ring rotates about its axis with a constant frequency f (revolution per second). The magnetic induction at the centre of the ring is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → μ0qf ÷ 2R
A charge moving round a circle is a current loop. The whole charge q passes any point of the ring once per revolution, that is, f times per second.
\( \displaystyle I = \frac{q}{T} = qf \)
The field at the centre of a circular loop is
\( \displaystyle B = \frac{\mu_0 I}{2R} \)
\( \displaystyle B = \frac{\mu_0 q f}{2R} \)